1. Field of the Invention
The present invention relates to an optical transmitting/receiving method and apparatus and more particularly to an optical transmitting/receiving method and apparatus wherein optical parts and electronic parts are mounted on the same substrate.
2. Description of Related Art
With rapid progress of IC (Integrated Circuit) technology and LSI (Large Scale Integrated Circuit) technology, the operating speed and integration density of these circuits have been improved, thereby accelerating improvement in performance of MPU (Micro-Processing Unit: Microprocessor) and of operation rate and capacity of memory chip. Under the situation explained above, particularly in the case of high speed digital signal transmission and in the case where a high speed bus or the like is required between MPU and memory chip, delay by the electrical wiring and deterioration of crosstalk due to the high speed and high density transmission by signal wire have been bottle neck for realization of higher performance. As the technique for solving such problem, attention is paid to optical wiring (optical inter-connection).
This optical wiring may be thought applicable in various levels, for example, between apparatuses, boards in the apparatus, chips in the board, etc. For signal transmission in comparatively short distance, for example, between chips, an optical transmitting/receiving method using optical waveguide as the transmission path has been effective.
An example of the optical transmitting/receiving method of the related art using such optical waveguide as the transmission path will be explained with reference to FIG. 1 and FIG. 2. Here, FIG. 1 is a schematic cross-sectional view illustrating an example of the optical transmitting/receiving system of the related art of FIG. 1, while FIG. 2 is an enlarged view of optical waveguide and 45.degree. micro-mirror of the optical transmitting/receiving method of FIG. 1.
As illustrated in FIG. 1, on the upper surface of a multilayer substrate 70 on which the first to fourth insulating layers 70a, 70b, 70c, 70d are sequentially laminated, a couple of plane type optical emitting/receiving elements 72a, 72b are face-down mounted with the flip chip joining method, namely mounted with the optical emitting/receiving surface directed downward.
Although not illustrated, a wiring layer is also formed at the upper surface and lower surface of the multilayer substrate 70 and between the first to fourth insulating layers 70a, 70b, 70c, 70d and moreover these wiring layers are connected through holes formed to the first to fourth insulating layers 70a, 70b, 70c, 70d, to form a multilayer wiring structure as a whole. Moreover, on the upper surface of multilayer substrate 70, optical emitting drive and optical receiving and amplifying circuit, LSI circuit and electronic parts such as inductor, capacitor and resistor or the like are mounted in addition to the plane type optical emitting/receiving elements 72a, 72b, utilizing the flip chip joining method and wire bonding joining method.
Moreover, on the upper surface of the multilayer substrate 70, an optical waveguide 74 is formed extending in straight up to the area just under the plane type optical emitting/receiving element 72b from the area just under the plane type optical emitting/receiving element 72a. As illustrated in FIG. 2, this optical waveguide 74 is formed of core 76 at the center for transmitting optical signal and clad 78 consisting of a material having a refraction index which is lower than that of core 76 in order to surround the core 76. Moreover, at both end faces of this optical waveguide 74, the 45.degree. micro-mirrors 80a, 80b and formed.
In the optical transmitting/receiving method illustrated in FIG. 1 and FIG. 2 as explained above, an optical signal emitted from an optical emitting surface, for example, of the plane type optical emitting/receiving element 72a is totally reflected in 90 degrees by the 45.degree. micro-mirror 80a located at the area just under the optical emitting surface. Thereafter, this optical signal is incident to the core 75 of the optical waveguide 74 and is then propagated within the core 76. Moreover, the optical signal propagated within the core 76 of this optical waveguide 74 is totally reflected in 90 degrees by the 45.degree. micro-mirror 80b and thereafter it is then incident to the optical receiving surface of the plane type optical emitting/receiving element 72b located at the area just above this 45.degree. micro-mirror 80b.
The optical signal emitted from the plane type optical emitting/receiving element 72a is then transmitted to the plane type optical emitting/receiving element 72b via the 45.degree. micro-mirror 80a, optical waveguide 74 and 45.degree. micro-mirror 80b. In the same manner, the optical signal emitted from the plane type optical emitting/receiving element 72b is then transmitted to the plane type optical emitting/ receiving element 72a via the 45.degree. micro-mirror 80b, optical waveguide 74 and 45.degree. micro-mirror 80a.
In FIG. 2, the optical signal is totally reflected in 90 degrees by the 45.degree. micro-mirror 80a and is then propagated within the core 76 of the optical waveguide 74. This profile is indicated using arrow mark as the image of optical transmission. This image of optical transmission is only tentative indication for convenience of explanation. Actually, it is a matter of course that the optical signal incident in the range of predetermined critical angle is propagated by repeating total reflection at the interface of the core 76 and clad 78 of the optical waveguide 74.
Moreover, in some cases, a very small size mirror illustrated in FIG. 3 is used in place of the 45.degree. micro-mirrors 80a, 80b illustrated in FIG. 1 and FIG. 2. Namely, on the upper surface of the multilayer substrate 70, the optical waveguide 82 extending in straight up to the other plane type optical emitting/receiving element from one plane type optical emitting/receiving element is formed. This optical waveguide 82 is also formed of the center core 84 for transmitting optical signal and clad 86 composed of a material having the refraction index lower than that of the core 84 to surround this core 84. The small size mirror 88 is also formed on the upper surface of the multilayer substrate 70 which is neighboring to one end face of this optical waveguide 82 and is located at the area just under the optical emitting surface of one plane type optical emitting/receiving element. In addition, although not illustrated, such small size mirror is also formed on the upper surface of the multilayer substrate 70 which is neighboring to the other end face of the optical waveguide 82 and is located at the area just under the receiving surface of the other plane type optical emitting/receiving element.
In this case, the optical signal, for example, emitted from the optical emitting surface of one plane type optical emitting/receiving element is totally reflected in 90 degrees by the 45.degree. mirror surface 90 of small size mirror 88 and thereafter the signal is then incident to the core 84 of the optical waveguide 82 and is then propagated within the core 84. Moreover, the optical signal propagated within the core 84 of the optical waveguide 82 is totally reflected in 90 degrees by the 45.degree. mirror surface of small size mirror (not illustrated) and thereafter it is incident to the optical receiving surface of the other plane type optical emitting/receiving element located at the area just above the mirror.
Next, the other example of the optical transmitting/receiving system of related art using the optical waveguide as the transmission path will be explained with reference to FIG. 4. Here, FIG. 4 is a schematic cross-sectional view illustrating the other example of the optical transmitting/receiving system of the related art. The elements like the structural elements in the optical transmitting/receiving method illustrated in FIG. 1 are designated by the like reference numerals and the same explanation is omitted here. Moreover, an enlarged view of optical waveguide and 45.degree. micro-mirror of the optical transmitting/receiving method of FIG. 4 are basically identical to FIG. 2. Therefore, such enlarged view is not illustrated.
As illustrated in FIG. 4, at the upper surface of the multilayer substrate 70 on which the first to fourth insulating layers 70a, 70b, 70c, 70d are sequentially laminated, the plane type optical emitting/receiving element 92 is face-down mounted by the flip chip joining method. Moreover, at the bottom surface of recessed area formed on the multilayer substrate 70, the end-face type optical emitting/receiving element 94 is mounted via the die pad with the wire bonding joining method.
In addition, on the upper surface of the multilayer substrate 70, an optical waveguide 96 extending up to the end face of the end face type optical emitting/receiving element 94 from the area just under the plane type optical emitting/receiving element 92 is also formed. At the end face in the side of the plane type optical emitting/receiving element 92 of this optical waveguide 96, the 45.degree. micro-mirror 98 is formed.
In this optical transmitting/receiving method illustrated in FIG. 4, the optical signal emitted, for example, from the optical emitting surface of the plane type optical emitting/receiving element 92 is totally reflected in 90 degrees by the 45.degree. micro-mirror 98 located at the area just under the optical emitting surface and thereafter propagated within the optical waveguide 96. The optical signal propagated within the optical waveguide 96 is then incident to the optical receiving surface of the end-face type optical emitting/receiving element 94.
The optical signal emitted from the plane type optical emitting/receiving element 92 as explained above is then transmitted to the end-face type optical emitting/receiving element 94 via the 45.degree. micro-mirror 98 and optical waveguide 96. In the same manner, the optical signal emitted from the end-face type optical emitting/receiving element 94 is also transmitted to the plane type optical emitting/receiving element 92 via the optical waveguide 96 and 45.degree. micro-mirror 98.
Here, it is also possible to use a small size mirror in place of the 45.degree. micro-mirror 98 as explained with reference to FIG. 3. Therefore, the same figure and explanation will be omitted here.
In the optical transmitting/receiving method using the optical waveguide of the related art as the transmission path, electronic parts such as optical emitting drive and receiving circuit, LSI circuit, inductor, capacitor and resistor are mixed in mounting in addition to the plane type optical emitting/receiving elements 72a, 72b, 92 and end-face type optical emitting/receiving element 94 on the upper surface of the multilayer substrate 70 having the multilayer wiring structure. Moreover, optical wiring section such as optical waveguides 74, 96 for optically connecting the plane type optical emitting receiving elements 72a, 72b, plane type optical emitting/receiving element 92 and end-face type optical emitting/receiving element 94 and electrical joining section for mounting electronic parts by the flip chip mounting or wire bonding wiring method are also mixed in the arrangement.
As illustrated in FIG. 5, for example, on the occasion that electrical wiring sections 100a, 100b are formed on the upper and lower surfaces of the multilayer substrate 70 and the LSI circuit 102, for example, is flip-chip mounted via the flip chip bump 104 on the electrical wiring section 100a of this upper surface, a plurality of flip chip bumps 104 of the LSI circuit 102 are held by a plurality of lines of optical waveguide 106. Here, the optical waveguide 106 is formed linearly between a pair of optical emitting/receiving elements. Therefore, the optical wiring sections of optical waveguides 106 of a plurality lines extending linearly and electrical joining section of electronic parts such as LSI circuit 102 are mixed in the mounting format at a higher density.
Therefore, on the occasion that various electronic parts such as LSI circuit 102 are mounted, for example, by the flip chip joining method or wire bonding joining method on the upper surface of the multilayer substrate 70, there is a problem that degree of freedom for arrangement of electronic parts is restricted by the optical wiring section such as optical waveguide 106 of a plurality of lines extending linearly and thereby high density and highly efficient mounting can no longer be realized.
Moreover, as illustrated in FIG. 5, when the LSI circuit 102, for example, is mounted to the electrical wiring section 100a via the flip chip bump 104, a part of the surface of electrical wiring section 100a must be exposed. Therefore, the clad 110 of the optical waveguide 106 formed of the center core 108 and surrounding clad 110 must be cut and opened. For this reason, not only the manufacturing process is complicated but also reliability of optical waveguide 106, moreover, reliability of the optical transmitting/receiving method may be deteriorated.
Since the 45.degree. micro-mirrors 80a, 80b, 98 formed at the end faces of the optical waveguides 74, 96 have the inverse trapezoidal shape in its cross-sectional view, the ordinary method for mechanically cutting the optical waveguides 74, 96 cannot be used and therefore dry-etching technique must be used. Therefore, here rises a problem that manufacturing process is complicated and manufacturing cost may also be raised.
As illustrated in FIG. 3, small size mirror 88 may also be formed adjacent to the end face of optical waveguide 82 in place of the 45.degree. micro-mirrors 80a, 80b, 98. Even in this case, since the small size mirror 88 must be formed through accurate alignment at the area just under the plane type optical emitting/receiving elements 72a, 72b, 92, also rises a problem that manufacturing process is also complicated and manufacturing cost also rises.